Rare Earth Ion Doping Research Articles

Rare-earth-size effects on thermoluminescenceand second-harmonic generation

The substitution of rare-earth ions into insulating host crystalsintroduces lattice strains and, for non-trivalent sites, a need forcharge compensation. Such effects alter the site symmetry and thisis reflected in properties such as the wavelength,linewidth, lifetime and relative intensity of the rare-earthtransitions. Equally clear, but less well documented, is theinfluence on second-harmonic generation (even from cubic crystallattices). For example, in bismuth germanate, second-harmonicgeneration efficiency varies by factors of more than 100 as a resultof different rare-earth dopant ions. The ions are variouslyincorporated as substitutional ions, pairs, clusters, or even asprecipitates of new phases, but the detailed modelling is oftenspeculative. This article summarizes some recent studies whichexplore the role of rare-earth ions in thermoluminescence and second-harmonic generation. There are numerous differences in glow peaktemperature, for nominally the same defect sites, which are thoughtto indicate charge trapping and recombination within coupled defectsites, or within a large complex. Size and cluster effects can bemodified by heat treatments. This review considers the similarityand trends seen between numerous host lattices which are doped withrare-earth ions. For thermoluminescence there are trends in thevariation in glow peak temperature with ion size, with movements of20 to 50 K. Examples are seen in many hosts with extremeeffects being suggested for zircon, with peak shifts of 200 K(probably from precipitate phases).

Photoluminescence spectra of CuAlS 2 doped with Er

Detailed photoluminescence (PL) spectra of CuAlS 2 doped with Er (and Fe) are observed at various temperatures and pressures. Both broad PL derived from host material CuAlS 2 and sharp PL peaks derived from doped lanthanide ions exist in PL. Even at 2 K, there are more than 21 peaks in sharp PL assigned to transition from 4 S 3/2 to 4 I 15/2 . This indicates that Er 3+ ions exist under some different environments. When increasing the applied pressures, the fact that each peak shifts to lower energy is explained by increasing crystal fields and mixing of its higher energy states.

Role of segregating dopants on the improved creep resistance of aluminum oxide

Recent studies have demonstrated that p.p.m. levels of rare-earth dopant ions (e.g. Y, La, Nd) wield a beneficial and highly potent influence on the creep properties of alumina. In addition, codoping with ions of disparate sizes (Nd, Zr) resulted in even further enhancement of the creep behavior. In all cases, the dopant ions were found to strongly segregate to grain boundaries. Creep rates were not influenced by the presence of second phase precipitates, verifying that the creep improvement is a solid solution effect. In an attempt to clarify the exact mechanism(s) that controls creep behavior of the doped aluminas, various advanced characterization techniques have been applied including: secondary ion mass spectrometry, scanning transmission electron microscopy, orientation image microscopy, and extended X-ray absorption fine structure as well as atomistic computer simulation and studies of the creep kinetics. Although no definitive mechanism has been established, a logical explanation is that outsize ions segregate to more energetically favorable grain boundary sites, and improve creep resistance by blocking a few critical diffusive pathways. This mechanism is sufficiently general that it may be applicable to other ceramic systems.

Extended Defect Models for Thermoluminescence

Thermoluminescence modelling started with very simple models of highly localised point defects, and separation of trapping and recombination centres. Whilst these ideas still dominate the discussions, current research indicates that most defects are far more complex, with localised transitions, and defect interactions extending over many lattice. sites. Multi-ion defect sites have been clearly established for LiF dosemeters and, similarly, models to account for charge compensation and lattice distortion of rare earth dopant ions (e.g. in CaF 2 , CaSO 4 etc.) all include the possibility of large complex recombination sites. Data obtained from thermoluminescence emission spectra indicate that ions can interact directly by coupling between the trapping and recombination sites Further, the thermoluminescence dosimetry must originate within different parts of the same large complex. Many examples support models of large complexes with internal transitions, including glow peak temperatures which differ with changes in rare earth ion dopants, where the peak shifts are determined by the ionic radii of the rare earth ions. Examples are presented which emphasise that thermoluminescence is often generated by internal charge transfer within very large defect complexes.

Rare earth fluorescence in NASICON type phosphate glass, Na3TiZnP3O12

The emission spectra of Pr3+, Eu3+ and Dy3+ doped in NASICON type phosphate glass, Na3TiZnP3O12 (NTZP) are studied. The dopant rare earth ions occupy sites with 8–9 coordination in a highly covalent environment. For Pr3+ ion, calculated and observed branching ratios for lasing transitions3 P 0→3 H 4,6 agree well and found to be 0·64 and 0·24, respectively. The emissions of Pr3+ show strong temperature dependence on account of Boltzmann population of the higher excited states at room temperature. The excitation spectrum of Eu3+ gives rise to phonon assisted side band for5 D 2←7 F 0 transition at higher energy side with a phonon energy maximum of 1022 cm−1 and an electron phonon coupling strength (g) of 0·018. The value of phonon energy maximum agrees with infrared spectral data. The results show that observation of high energy emissions in phosphate glasses require much higherg values. The red/orange and yellow/blue transitions of Eu3+ and Dy3+, respectively show that the Eu3+ occupy more distorted site than Dy3+.

In Situ Dehydroxylation in Eu3+-Doped Sol−Gel Silica

Fluorescence line narrowing and lifetime measurements are used to characterize the extents of clustering and hydroxyl quenching, respectively, in Eu3+-doped sol−gel silica glasses prepared using europium trifluoromethanesulfonate (triflate). A triflate ((CF3SO3)3Eu) rather than a traditional nitrate (Eu(NO3)3·6H2O) precursor is used as the rare earth ion dopant in order to determine the feasibility of effecting chemical dehydroxylation via in situ fluorination by incorporating fluorine directly as a ligand substituent of the Eu3+ precursor. In samples doped only with Eu3+, the use of the triflate precursor leads to no noticeable differences in hydroxyl quenching of Eu3+ fluorescence or Eu3+ aggregation relative to samples prepared with a nitrate precursor. Beneficial effects are observed, however, in samples codoped with Al3+ or Sr2+. When Al3+ or Sr2+ is included in the synthesis, a reduction in hydroxyl quenching of Eu3+ is observed when the triflate precursor is used relative to the nitrate precursor. ...

Irradiation Damage on BaLiF3 Crystallites and Its Suppression by Rare‐Earth Ion Doping

The x‐ray and γ‐ray induced damage in crystallites and its suppression by rare earth ion doping have been studied by electron spin resonance and thermally stimulated luminescence methods. It has been found that the x‐ray irradiation damage is light and can be erased easily. This shows that the crystallite is an ideal host for x‐ray storage material. But the damage induced by γ‐ray has been found to be relatively hard to recover, however the γ‐ray irradiation hardness can be improved by rare earth (e.g., ) ion doping. So the is also promising material for being used in detection of high‐energy particles (e.g., γ‐ray).

Traps in SrAl 2O 4:Eu 2+ phosphor with rare-earth ion doping

The depths and relative densities of the traps in a series of SrAl 2O 4:Eu 2+, Ln (14 rare-earths) phosphors are measured with a transient luminescence method. The observed hole activation energies (trap depths) are quite different across the series and related to the ionization potential and 4f n -4f n−1 5d transition energies of the divalent ions of this series, reflecting the 4f-electron interaction energy of each rare earth ion.

Spectroscopic properties of Nd3+& Eu3+ions in heavy metal fluoride (ZrF4& InF3) glasses

Abstract Physical properties, optical absorption, photoluminescence spectra and the lifetimes of the fluorescent states of the dopant rare earth ions (Nd3+ & Eu3+) in newly prepared ZrF4 and InF3 based heavy metal fluoride glasses have been studied. By the application of Judd-Ofelt theory, the spectral intensities of the absorption spectra have been analysed and the resulting data have been used in understanding the fluorescence properties of the glasses studied. From the measured and calculated lifetimes of the fluorescent states, the quantum efficiencies have been evaluated to understand the effects of the glass network modifiers in assessing the optical quality of the materials investigated.

A review of fluoride fibres for optical amplification

This paper reviews the current world-wide status of fibres based on the fluoride glass system for optical amplification, with particular emphasis on telecom applications. The key feature of fluorozirconate glasses, with the very long wavelength multiphonon edge, is the accompanying relatively low non-radiative decay rate of excited rare-earth dopant ions. This gives unique opportunities compared with the better known oxide glass systems. Amplifiers with high gains have been demonstrated at important wavelengths such as 0.8, 1.3 and 1.5 μm. Improvements to allow the fabrication of more efficient fibres are also discussed.

A structural study of the glass matrix of phosphosilicate optical fibre cores highly doped with rare-earth ions

The microstructure of high phosphate content (∼ 17 mol%) optical fibre preform cores fabricated by the condensation of phosphoric acid within a porous silica frit has been investigated. The core regions of a number of optical fibre preforms were analysed using 31P magic angle spinning nuclear magnetic resonance spectroscopy and small spot X-ray photoelectron spectroscopy. The presence of polymerised phosphate chains indicates an inhomogeneous glass structure. The influence of this heterogeneity on fibre loss and the spectral broadening characteristics of incorporated rare-earth dopant ions is discussed.

ENHANCEMENT IN A Ho3+–Yb3+ QUANTUM COUNTER BY ENERGY TRANSFER

In all the infrared quantum counter systems reported to date, a single rare-earth ion dopant was used as the activator. This limits the optimum concentration to about 1%, since above this value nonradiative processes begin to dominate. In order to increase the number of ions which can absorb the infrared signal Yb3+ was used as a sensitizer. By making use of the energy transfer from Yb3+ to Ho3+ the green quantum counter fluorescence was increased by more than two orders of magnitude.